Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$51.38	11.384%	$57.2291	$57.23	$57.25	$57.20
Purchase #2	$38.47	9.567%	$42.1504	$42.15	$42.15	$42.20
Purchase #3	$160.56	4.292%	$167.4512	$167.45	$167.45	$167.50
Purchase #4	$105.90	3.235%	$109.3259	$109.33	$109.35	$109.30
Purchase #5	$123.50	3.257%	$127.5224	$127.52	$127.50	$127.50
Purchase #6	$43.44	6.138%	$46.1063	$46.11	$46.10	$46.10
Purchase #7	$131.86	4.241%	$137.4522	$137.45	$137.45	$137.50
7 purchase totals =	$655.11		$687.2375	$687.24	$687.25	$687.30